The invention relates to the synthesis of polybenzoxazole (PBO), polybenzimidazole (PBI) or polybenzothiazole (PBT) and related polymers (hereinafter referred to as PBZ polymers).
AA/BB-PBZ polymers are a known class of polymers which contain a plurality of mer units comprising:
(1) a first aromatic group (Ar.sup.1), PA0 (2) a first azole ring which is fused with the first aromatic group, PA0 (3) a second azole ring which is fused with the first aromatic group, and PA0 (4) a divalent organic group (DL), which is inert with respect to all reagents for making PBZ polymers under polymerization conditions, bonded by a single bond to the 2-carbon of the second azole ring. PA0 DL is a divalent organic group as previously described: and PA0 each Z is independently chosen from the group consisting of --O--, --S-- or --NR--, wherein R is an aliphatic or aromatic group which does not interfere with polymerization. PA0 (1) a first aromatic group (Ar.sup.1): PA0 (2) a first o-amino-basic moiety containing: PA0 (a) a primary amine group bonded to the first aromatic group, and PA0 (b) a hydroxy, thio or amine group bonded to the first aromatic group in ortho position with respect to the primary amine group: and PA0 (3) a second o-amino-basic moiety bonded to the first aromatic group, PA0 (1) a divalent organic moiety (DL) which is inert with respect to all reagents under reaction conditions: and PA0 (2) two "electron-deficient carbon groups," as that term is hereinafter defined, bonded to said divalent organic moiety (DL). PA0 (1) at least one BB-monomer ion: and PA0 (2) at least one phosphate ion PA0 (1) at least one BB-monomer ion: and PA0 (2) at least one phosphate ion PA0 (a) preparing a solution containing a mineral acid and a BB-monomer phosphate salt of substantially known BB-monomer content; and PA0 (b) contacting said BB-monomer in said mineral acid solution with an AA-monomer in an amount and under conditions such that a PBZ polymer is formed.
Mer units are preferably linked by a single bond from the divalent organic group (DL) to the the the 2-carbon in the first azole group of an adjacent unit.
Mer units in AA/BB-PBZ polymers preferably comply with Formula 1 ##STR1## wherein: Ar.sup.1 is a first aromatic group as previously described:
PBZ polymers, their chemical structure, their properties and their synthesis are described in depth in a number of references such as 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles. 601 (J. Wiley & Sons 1988): Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products. U.S. Pat. No. 4,703,103 (Oct. 27, 1987): Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S. Pat. No. 4,578,432 (Mar. 25, 1986); Wolfe et al., Liquid Crystalline Poly(2,6-Benzothiazole) Compositions, Process and Products, U.S. Pat. No. 4,533,724 (Aug. 6, 1985); Wolfe, Liquid Crystalline Polymer Compositions, Process and Products. U.S. Pat. No. 4,533,693 (Aug. 6, 1985) and Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985), which are incorporated herein by reference.
AA/BB-PBZ polymers are synthesized by the reaction of a BB-monomer comprising:
and an AA-monomer comprising:
BB-monomers are extremely sensitive to air oxidation in their free amine state. For that reason, BB-monomers are typically isolated and stored as hydrogen chloride salts, which are more stable. See Chenevey et al., Process for Preparing Shaped Articles of Rigid Rod Heterocyclic Liquid Crystalline Polymers, U.S. Pat. No. 4,606,875 (Aug. 19, 1986) at Column 4, lines 29-49; and Choe, Process for the Production of High Molecular Weight Para Ordered Aromatic Heterocyclic Polymer, U.S. Pat. No. 4,423,202 (Dec. 27, 1983) at Column 3, lines 1-10.
The hydrogen halide salts of BB-monomers are difficult to polymerize, so that the hydrogen halide is removed from the monomer in a "dehydrohalogenation step" prior to polymerization. See, e.g., Choe, Process for the Production of High Molecular Weight Para Ordered Aromatic Heterocyclic Polymer, U.S. Pat. No. 4,423,202 (Dec. 27, 1983) at Column 4, lines 38-52. The dehydrohalogenation step causes the release of two moles of hydrogen halide gas, typically hydrogen chloride gas, for each mole of monomer reacted. The gas is corrosive and limits the materials from which equipment can be made. Furthermore, the gas causes substantial foaming in the thick solutions used for the synthesis of PBZ polymers. Foaming reduces the efficiency of mixing in the system, which must be vigorous to form high molecular weight polymer, and necessitates the use of reaction vessels having sufficient extra volume to accommodate the foam. Finally, the dehydrohalogenation step is time consuming and lowers the economic efficiency of the PBZ polymerization.
Prior art processes have relied upon elaborate staging processes to minimize the foaming within manageable limits. See Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987) at column 53, line 55 to column 56, line 4; Wolfe, Liquid Crystalline Polymer Compositions, Process and Products. U.S. Pat. No. 4,533,693 (Aug. 6, 1985) at column 42, line 61 to column 44, line 66: and Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985) at column 39, line 59 to column 42, line 11, which are incorporated herein by reference. Those processes do not eliminate foaming. They eliminate neither the need to use specific materials in the equipment nor the need to take the time for dehydrohalogenation.
What is needed is a process for forming a reactive solution of BB-monomer in mineral acid which does not require a dehydrohalogenation step.